The present invention relates generally to convolving circuits, such as those used in radar pulse compression applications. Specifically, the present invention relates to convolving circuits which are suitable for incorporation within an integrated circuit. More specifically, the present invention relates to an architecture of a convolving circuit element which permits expansion while minimizing external connections between convolving elements.
Conventional convolving circuits are known by those skilled in the art to add a signal with portions of itself that are shifted in time. In digital convolvers the signal may be digitized into many digital samples and each of the samples may be encoded using a predetermined number of bits. Accordingly, while the convolving process represents a type of arithmetic addition operation, a large number of bits per sample together with a large number of samples conventionally require implementation of a convolution circuit in a relatively large amount of hardware.
Such convolver circuits may be used, for example, in radar applications which include a pulse compression function. These applications encode a transmitted radar pulse by shifting the phase of the transmitted radar pulse in a defined manner. In binary phase (bi-phase) coding the transmitted radar pulse is divided into a predetermined number of equal duration segments called chips. Each chip of the transmitted radar pulse exhibits one of two phase values. Each of these two phase values represents 180.degree. phase shift relative to the other. A code, such as a well-known Barker code, various Gold codes, or the like, defines the phase coding of the transmitted pulse. A received echo signal also exhibits this phase coding. The received signal may be decoded using the same code in a convolution process so that the received pulse is compressed and reshaped to be more useful for post-convolution processing in a radar device. The pulse compression permits the radar to discriminate between objects located close to each other and to receive the benefits of a short pulse without requiring the instantaneous power which would otherwise be needed.
Conventional digital convolution circuits tend to be expensive, relatively unreliable, and to require a large amount of power and a large volume for their implementation. Although those skilled in the art recognize that digital circuits in general may be implemented within an integrated circuit, significant problems are encountered in defining an architecture for such an integrated circuit that is flexible enough to meet a wide variety of applications and yet is sufficiently small to fit within available integrated circuit area. If the application requires more circuitry than fits within a single integrated circuit, then additional problems arise due to minimizing terminals for interconnections between the various integrated circuits.